by Ann » Sun Apr 26, 2015 11:13 pm
Chris Peterson wrote:starsurfer wrote:Although it is false colour, I don't mind as it looks so pretty! A
true colour image would show it to be red and pink.
True color images show just about everything to be shades of pink, because of the way hydrogen dominates. About all we see is H alpha and continuum light, with maybe a little green from oxygen. That's why we don't see so many natural color images from HST. They hide too much information. To really see and understand something, we usually need to look at narrowband emissions. That this happens to also be pretty is just an added bonus!
Some planetaries look very green (or blue, or turquoise) in RGB images. In other words, some planetaries are dominated by OIII emission. The fine RGB image of the Ant Nebula (thanks for the link, starsurfer!) shows it to be totally dominated by hydrogen, and that is not a given at all when it comes to planetaries.
Does anyone have any sort of explanation as to why some planetaries are so dominated by oxygen and others so dominated by hydrogen? I can't help thinking of the extragalactic objects similar to
Hanny's Voorwerp, which glow green from OIII, and which have been ionized by energetic quasar jets.
(And by the way... I find the pink RGB image of the Ant Nebula, set among differently-colored stars, more beautiful than the HST image. But that is just a matter of taste.)
Ann
[quote="Chris Peterson"][quote="starsurfer"]Although it is false colour, I don't mind as it looks so pretty! A [url=http://www.chart32.de/index.php/component/k2/item/69]true colour image[/url] would show it to be red and pink.[/quote]
True color images show just about everything to be shades of pink, because of the way hydrogen dominates. About all we see is H alpha and continuum light, with maybe a little green from oxygen. That's why we don't see so many natural color images from HST. They hide too much information. To really see and understand something, we usually need to look at narrowband emissions. That this happens to also be pretty is just an added bonus![/quote]
Some planetaries look very green (or blue, or turquoise) in RGB images. In other words, some planetaries are dominated by OIII emission. The fine RGB image of the Ant Nebula (thanks for the link, starsurfer!) shows it to be totally dominated by hydrogen, and that is not a given at all when it comes to planetaries.
Does anyone have any sort of explanation as to why some planetaries are so dominated by oxygen and others so dominated by hydrogen? I can't help thinking of the extragalactic objects similar to [url=https://galaxyzooblog.files.wordpress.com/2012/02/hv-o3ha.jpg]Hanny's Voorwerp[/url], which glow green from OIII, and which have been ionized by energetic quasar jets.
(And by the way... I find the pink RGB image of the Ant Nebula, set among differently-colored stars, more beautiful than the HST image. But that is just a matter of taste.)
Ann